Basic physiological factors which modify rates of protein synthesis and degradation in lung tissue are being investigated. For these studies, a new preparation for perfusion of rat lungs in situ was developed and proven stable and metabolically active using a biochemical approach. The role of hormones (especially insulin), amino acids, and other substrates and of physiological parameters in the control of protein turnover is being evaluated, along with the effects of other factors to which the lungs may be frequently exposed (e.g., volatile anesthetics). Furthermore, the extent to which alterations in protein synthetic or degradative rates contribute to rapid ling growth following unilateral pneumonectomy is under investigation. In addition to alterations in the metabolism of whole lung proteins, turnover of specific lung proteins is under study, especially those proteins known to play an important role in maintenance of normal lung structure and function.